Physical Processes

Tidal Flushing

Tidal flushing (the movement of water in and out of a water body due, in part, to tidal processes) has important water quality implications that are known to affect numerous estuarine management issues. To develop tidal flushing categories, residence times (the average length of time that a parcel of water remains in an estuary) for water bodies in the Virginia coastal zone were calculated using three water quality models, depending upon the complexity of the water body. Results showed that residence times range from 0.1 to 29 days (with one outlier of 72 days). Approximately 80% of water bodies in the Virginia coastal zone are dominated by quickly flushed tidal creeks and tributaries with residence times less than about 5 days.

Residence times were grouped into tidal flushing categories using mean depth. Shallower water bodies flush more quickly than deeper water bodies. The flushing categories (quickly, intermediately, and slowly flushed) reflect a relative time frame in which a water body is flushed. Residence times and flushing categories were joined to a geographic information system layer in order to spatially display and analyze results.